A VLA Study of High-redshift GRBs. II. The Complex Radio Afterglow of GRB 140304A: Shell Collisions and Two Reverse Shocks
A VLA Study of High-redshift GRBs. II. The Complex Radio Afterglow of GRB 140304A: Shell Collisions and Two Reverse Shocks
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DOI：
10.3847/1538-4357/aabfd8
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发表时间：
2017-07
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影响因子：
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通讯作者：
T. Laskar;E. Berger;R. Margutti;A. Zauderer;P. Williams;W. Fong;R. Sari;K. Alexander;A. Kamble
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作者：
T. Laskar;E. Berger;R. Margutti;A. Zauderer;P. Williams;W. Fong;R. Sari;K. Alexander;A. Kamble
我们提供了 GRB 140304A 在 z = 5.283、从 1 到 86 GHz、从 0.45 到 89 天的详细多频率、多历元射电观测。无线电和毫米波数据表现出不寻常的多光谱成分，这不能用标准的正向和反向冲击场景来简单解释。通过从无线电到 X 射线的详细多波长分析，我们将前向激波参数限制为 Ek,iso ≈ 4.9 × 1054 erg、A * ≈ 2.6 × 10−2、ϵ e ≈ 2.5 × 10−2、ϵ B ≈ 5.9 × 10−2、p ≈ 2.6 和 θ jet ≈ 1.°1，得到射束校正的 γ 射线和动能分别为 E γ ≈ 2.3 × 1049 erg 和 E K ≈ 9.5 × 1050 erg。我们将过量射电发射建模为由壳碰撞发射的后期反向激波 (RS) 和标准 RS 或衍射星际闪烁 (ISS) 的组合，后者也会在约 0.26 天时在 X 射线中产生重新增亮。在标准 RS 解释下，我们调用正向和反向激波之间的一致性参数来推导减速时间 tdec ≈ 100 s、喷射物洛伦兹因子 Γ(tdec) ≈ 300 和低 RS 磁化强度 RB ≈ 0.6。我们的观测结果强调了射电观测在捕获RS发射方面的力量，从而限制了GRB喷出物和中央发动机的特性，以及国际空间站在最终识别GRB射电余辉中RS发射方面提出的挑战。
We present detailed multifrequency, multiepoch radio observations of GRB 140304A at z = 5.283 from 1 to 86 GHz and from 0.45 to 89 days. The radio and millimeter data exhibit unusual multiple spectral components, which cannot be simply explained by standard forward and reverse shock scenarios. Through detailed multiwavelength analysis spanning radio to X-rays, we constrain the forward shock parameters to Ek,iso ≈ 4.9 × 1054 erg, A * ≈ 2.6 × 10−2, ϵ e ≈ 2.5 × 10−2, ϵ B ≈ 5.9 × 10−2, p ≈ 2.6, and θ jet ≈ 1.°1, yielding a beaming-corrected γ-ray and kinetic energy, E γ ≈ 2.3 × 1049 erg and E K ≈ 9.5 × 1050 erg, respectively. We model the excess radio emission as due to a combination of a late-time reverse shock (RS) launched by a shell collision, which also produces a rebrightening in the X-rays at ≈0.26 days, and either a standard RS or diffractive interstellar scintillation (ISS). Under the standard RS interpretation, we invoke consistency arguments between the forward and reverse shocks to derive a deceleration time, tdec ≈ 100 s, the ejecta Lorentz factor, Γ(tdec) ≈ 300, and a low RS magnetization, RB ≈ 0.6. Our observations highlight both the power of radio observations in capturing RS emission and thus constraining the properties of GRB ejecta and central engines and the challenge presented by ISS in conclusively identifying RS emission in GRB radio afterglows.